The macchiato is a cornerstone of Italian coffee culture, along with the espresso and cappuccino, among other coffee drinks.
It’s basically an espresso (served in a demitasse cup) with a spot of foamed milk or cream on top — the name macchiato means "Spotted.”
So really, you could look at it as a cross between an espresso and a cappuccino.
Since Italians tend to only drink cappuccino in the morning, a macchiato gives the afternoon drinker the option of having a little milk in their espresso for some extra flavor.
It’s also a good option for those who can’t tolerate a strong espresso but find a cappuccino too weak and milky.